New virus cases are rising on some Caribbean islands, the W.H.O. says.

Bucking the trend in much of the Americas, several Caribbean countries are reporting significant surges in known coronavirus infections, World Health Organization officials warned on Wednesday.

Reports of new cases are up 40 percent over the last week in the Dominican Republic and Barbados, said Dr. Carissa F. Etienne, the director of the Pan American Health Organization, a division of the W.H.O.

“In fact,” Dr. Etienne said at a news conference, “half of Barbados’s cumulative Covid infections since the pandemic began have been reported in the last month.”

Cases are also rising in Trinidad and Tobago and some smaller island nations and territories in the region, including St. Martin, St. Kitts and Nevis, Anguilla and the Cayman Islands.

Many Caribbean countries have had difficulty moving quickly with vaccination efforts, both because of difficulty obtaining doses and because of widespread public hesitancy.

“It really troubles me that some of my Caribbean brothers and sisters have been slow to accept the Covid-19 vaccines that have been made available to them,” said Dr. Etienne, who is from Dominica.

Across Latin America and the Caribbean, 41 percent of the population has been fully vaccinated against Covid-19, according to the Pan American Health Organization.

New case reports are declining across North America, and infections and deaths are declining in most of Central America. The picture is also improving in South America, with the exception of Bolivia and Venezuela, the organization said.

Dr. Etienne said it was important for countries in the region to build up testing even as reports of new cases ebbed, so that any fresh outbreaks could be caught before they developed into widespread surges. “More and more, we’re seeing how local hot spots are driving national trends,” she said.

A good approach, she said, would be to integrate surveillance for Covid-19 with monitoring of other respiratory viruses. She said her organization was working with the Centers for Disease Control and Prevention in the United States to develop a new protocol for P.C.R. testing that would screen the same samples for both Covid-19 and influenza.

Strong surveillance networks, she said, could also help detect emerging pathogens before they spread, and serve “as the region’s backbone for pandemic preparedness.”